1. Field of the Invention
The present invention relates to an image capture apparatus and a method of controlling the same and, more particularly, to an image capture apparatus having a continuous shooting function and a method of controlling the same.
2. Description of the Related Art
In recent years, a variety of image capture apparatuses capable of continuously performing focus adjustment of an imaging lens for a moving subject have been commercialized, so various methods for achieving continuous focus adjustment have been proposed. Examples of these methods include a method of performing continuous focus adjustment using signals not only from a focus detection area adjusted for the subject by the user but also from other focus detection areas among a plurality of focus detection areas (a method which increases the focus detection area), and a method of detecting (tracking) a motion of the subject by a subject recognition technique and performing focus adjustment at the position to which the subject has moved.
A digital still camera (to be simply referred to as a camera hereinafter) generally has a single-shooting mode and a continuous shooting mode, and often captures a subject which makes various motions in the continuous shooting mode. Also, a variety of conventional cameras perform metering, exposure calculation, focus detection, and focus adjustment of imaging lenses for each frame in consideration of changes in luminance and movement of the subject during continuous shooting. The above-mentioned techniques of detecting a motion of the subject allow optimum focus adjustment and exposure control for the subject.
However, the recent cameras are capable of continuous shooting at a speed as high as 10 or more frames per sec, so exposure calculation and focus adjustment of imaging lenses must be performed in a shorter period of time, resulting in an increase in probability that an exposure failure or a picture out-of-focus will occur.
Hence, Japanese Patent Laid-Open No. 2010-72283 captures image data of the first frame of shooting upon the same exposure calculation and focus alignment of an imaging lens as in single shooting, and captures image data of the second and subsequent frames upon detecting an area in which a specific subject is present from the image data of the first frame and configuring the storage time, exposure calculation range, and focus detection area in metering. In Japanese Patent Laid-Open No. 2010-72283, the inventor states that this operation achieves exposure calculation and focus adjustment in a short period of time, and allows stable exposure control and focus adjustment even during high-speed continuous shooting.
However, in Japanese Patent Laid-Open No. 2010-72283, since the metering range is configured based on the position information of the subject, the exposure calculation result may change even if the luminance of the subject remains unchanged when, for example, the relationship between the metering range and the subject position changes. Also, the technique described in this patent literature requires exposure calculation for each frame, and therefore makes processing cumbersome.
Japanese Patent Laid-Open No. 2003-255429 discloses an invention for preventing variations in exposure while omitting exposure calculation during continuous shooting. In Japanese Patent Laid-Open No. 2003-255429, the luminance values of the subject in the current and immediately previous frames are compared during continuous shooting. If the luminance of the subject remains unchanged, the control values of exposure in the immediately previous frame are continuously used in the current frame; otherwise, exposure calculation is performed. The method described in Japanese Patent Laid-Open No. 2003-255429 can omit exposure calculation if the luminance of the subject remains unchanged, and prevent variations in exposure because the exposure value remains unchanged.
However, if the luminance considerably changes in the background, for example, if an extremely dark or bright object enters the background, the metered value (the field of view luminance) also changes, so exposure calculation is performed even if the luminance of the main subject remains unchanged in the method described in Japanese Patent Laid-Open No. 2003-255429. Especially in photochronography, it is often the case that the brightness of the background considerably changes even if the luminance of the main subject remains unchanged, so this problem is non-negligible. Also, when exposure calculation is performed even if the luminance of the main subject remains unchanged, exposure changes due, for example, to a change in positional relationship between the main subject and the metering range, leading to the occurrence of variations in exposure during continuous shooting, as in the invention described in Japanese Patent Laid-Open No. 2010-72283.